Item_ref's null_value wasn't updated in save_org_in_field() causing reported
error.


sql/item.h:
  Fix bug #14850 Item_ref's null_value wasn't updated
  Make save_org_in_field() update Item_ref's null_value.
mysql-test/r/view.result:
  Test case for bug #14850 Item_ref's null_value wasn't updated
mysql-test/t/view.test:
   Test case for bug #14850 Item_ref's null_value wasn't updated